The present invention relates to magnetic disk storage devices and more particularly to means for compressively clamping a plurality of magnetic disks to form a disk spindle assembly.
A major concern in magnetic disk spindle design is the manner in which the disk is clamped. The disks must be clamped with sufficient force to prevent radial movement that could result from imbalanced rotational forces, thermal expansion or shock/impact loads during shipping. To assure minimum radial shifting of the disks, the stack must be subjected to a specified clamping force. A typical method of applying force to the disk stack is the preloading of a clamping member against the stack using clamping screws. Use of screws for this purpose contributes to several problems. Screws must have sufficient tensile strength which normally requires the use of steel material having a lower coefficient of expansion than the aluminum component parts such as disks, spacers, and the hub. As a result, thermal cycling can cause stack clamping force variations and possibly permanent relaxation. Since only a limited number of screws can be used, the clamping force is not distributed evenly around the stack and peak forces at the screw locations contribute to disk distortion which causes increased axial runout and axial accelerations. The friction in the mating screw threads makes it difficult to determine how much of the tightening torque is being converted to an axial clamping force. This can contribute to additional force variation around the stack. Since screws involve metal-to-metal contact with large contact pressures, the assembly procedure can easily generate contaminating particles, especially when removal is required for rework or balancing. The thread tapping operation for multiple screw holes in the hub adds additional cost to the product.